diff --git a/CHANGELOG.md b/CHANGELOG.md
index fad689a..1501385 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## v3.8.5 (2026-10-21)
+
+### Security
+
+- Added `certifi>=2026.10.19` as a declared dependency so the CA bundle used by `requests` for stackql binary downloads no longer trusts `emSign ECC Root CA - G3`, the eMudhra root whose eight intermediate CA private keys were found to be recoverable in October 2026 (Mozilla Bugzilla 2083449, certifi advisory GHSA-6q48-6c7w-9gw2). pystackql ships no CA material of its own; this floor ensures fresh installs and upgrades resolve a patched bundle.
+- Added `tests/test_tls_trust.py` to assert the resolved certifi bundle excludes the compromised root (by certificate fingerprint) and that downloads never disable certificate verification.
+
 ## v3.8.4 (2026-06-29)
 
 ### Updates
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..7aab58f
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,29 @@
+**Note**:
+
+- All contributions to `pystackql`, through any means, are subject to the [license](/LICENSE).
+- This document itself and the patterns specified herein, are heavily influenced by [redis](https://github.com/redis/redis). We profusely thank the maintainers of same, from which we draw inspiration.
+- For useful information contributors **may** want to consider in developing `pystackql`, please see the "Building the package", "Testing Locally" and "Building the docs" sections of the [README](/README.rst), the [tests README](/tests/README.md), and the published documentation at [pystackql.readthedocs.io](https://pystackql.readthedocs.io).
+- All contributions to `pystackql` and actions related, through any means, are subject to the StackQL [CODE OF CONDUCT](https://github.com/stackql/stackql/blob/main/CODE_OF_CONDUCT.md).
+
+# Contribution flow
+
+Before beginning implementation work, please raise an issue (using the bug report, feature request or question template as appropriate) and receive a consensus that work should proceed.
+
+Please raise pull requests (PRs) from a fork of this repository. The richer the detail / evidence supplied, the easier the review process. A usefully named feature branch for the PR source is appreciated.
+
+PRs against `main` run the test suite on Linux, macOS and Windows across Python 3.9 to 3.13. Please keep changes working on all of them.
+
+## Development notes
+
+- `pystackql` is a Python wrapper around the `stackql` engine. Changes to the engine itself belong in [stackql/stackql](https://github.com/stackql/stackql), and provider definitions belong in the [stackql-provider-registry](https://github.com/stackql/stackql-provider-registry).
+- Run the non-server tests with `python run_tests.py`. Server-mode tests need a running `stackql srv` process (see `start-stackql-server.sh` or `start-stackql-server.ps1`), then `python run_server_tests.py`.
+- Tests use the no-auth Homebrew provider and provider-agnostic literal queries. Please do not add tests that require cloud credentials.
+- Runtime dependencies are declared in `pyproject.toml` as minimum versions rather than pins. Please keep it that way and avoid unrelated dependency bumps.
+- `README.rst` is reStructuredText and doubles as the PyPI readme. The documentation in `docs/` is built with Sphinx from the docstrings, so update the `StackQL.__init__` docstring when changing constructor parameters.
+- Releases bump `version` in `pyproject.toml` and add an entry to `CHANGELOG.md`.
+
+Finally, in respect of all your efforts; we thank you and ask that you please give us a star while you are at it.
+
+Many Thanks,
+
+The StackQL team.
diff --git a/SECURITY.md b/SECURITY.md
new file mode 100644
index 0000000..732b900
--- /dev/null
+++ b/SECURITY.md
@@ -0,0 +1,42 @@
+# Security Policy
+
+The StackQL team takes the security of `pystackql` seriously. We appreciate everyone who reports vulnerabilities responsibly, and we will do our best to acknowledge and address valid reports promptly.
+
+## Reporting a Vulnerability
+
+Please do not open a public GitHub issue for security reports. A public issue discloses the problem before a fix is available and puts users at risk.
+
+Instead, report privately using GitHub private vulnerability reporting:
+
+1. Open the [new advisory form](https://github.com/stackql/pystackql/security/advisories/new) (Security tab -> Advisories -> "Report a vulnerability").
+2. Provide as much detail as you can: affected `pystackql` version(s), Python version and operating system, reproduction steps, impact, and any suggested remediation.
+3. Submit. This opens a private advisory thread visible only to you and the maintainers.
+
+If you cannot use GitHub private vulnerability reporting, email us at [info@stackql.io](mailto:info@stackql.io). Please put "SECURITY" in the subject line and treat the contents as confidential.
+
+## Supported Versions
+
+Security fixes are applied to the latest released minor line, published to [PyPI](https://pypi.org/project/pystackql/). Older lines are supported on a best-effort basis only; we recommend upgrading to the latest release with `pip install --upgrade pystackql`. See the [changelog](/CHANGELOG.md) and the [PyPI release history](https://pypi.org/project/pystackql/#history) for the current version.
+
+| Version | Supported    |
+| ------- | ------------ |
+| 3.8.x   | Yes          |
+| < 3.8   | Best-effort  |
+
+`pystackql` supports Python 3.9 to 3.13 on Linux, macOS and Windows.
+
+## Response Expectations
+
+These are targets, not contractual guarantees:
+
+- We aim to acknowledge a report within a few business days.
+- We will keep you updated as we investigate and work on a fix.
+- We will coordinate disclosure timing with you once a fix or mitigation is ready.
+
+## Disclosure Policy
+
+We follow coordinated (responsible) disclosure. Please give us a reasonable opportunity to release a fix before any public disclosure. We are happy to credit reporters in the advisory and release notes, unless you prefer to remain anonymous.
+
+## Scope
+
+This policy covers the `pystackql` Python package in this repository as published to PyPI, including its Jupyter magic extensions. `pystackql` downloads and runs the `stackql` engine binary in local mode and connects to a `stackql` server in server mode; the engine, its binaries and its Docker images are maintained in [stackql/stackql](https://github.com/stackql/stackql) and covered by that repository's [security policy](https://github.com/stackql/stackql/blob/main/SECURITY.md). Provider definitions are maintained separately in the [stackql-provider-registry](https://github.com/stackql/stackql-provider-registry). Please report issues specific to those in their respective repositories.
diff --git a/pyproject.toml b/pyproject.toml
index e4a0337..886e35a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pystackql"
-version = "3.8.4"
+version = "3.8.5"
 description = "A Python interface for StackQL"
 readme = "README.rst"
 authors = [
@@ -25,6 +25,7 @@ classifiers = [
 requires-python = ">=3.9"
 dependencies = [
     "requests",
+    "certifi>=2026.10.19",
     "pandas",
     "IPython",
     "psycopg[binary]>=3.1.0",
diff --git a/requirements.txt b/requirements.txt
index 5270cf7..c69d776 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,7 @@
 # Core dependencies
 pandas>=1.3.0
 requests>=2.25.0
+certifi>=2026.10.19  # CA bundle without the compromised emSign ECC Root CA - G3 (eMudhra incident, Oct 2026)
 IPython>=7.0.0
 termcolor>=1.1.0
 PyYAML>=5.4.0
diff --git a/run_tests.py b/run_tests.py
index 9289308..e8f47ea 100644
--- a/run_tests.py
+++ b/run_tests.py
@@ -45,7 +45,8 @@ def main():
             "tests/test_output_formats.py",
             "tests/test_magic.py",
             "tests/test_async.py",
-            "tests/test_download.py"
+            "tests/test_download.py",
+            "tests/test_tls_trust.py"
         ])
    
     # Run pytest with the arguments
diff --git a/tests/test_tls_trust.py b/tests/test_tls_trust.py
new file mode 100644
index 0000000..5da7c0c
--- /dev/null
+++ b/tests/test_tls_trust.py
@@ -0,0 +1,110 @@
+# tests/test_tls_trust.py
+
+"""
+TLS trust store tests for PyStackQL.
+
+PyStackQL makes one outbound HTTPS call (downloading the stackql binary from
+releases.stackql.io via `requests`), and `requests` validates server
+certificates against the CA bundle shipped by `certifi`. These tests guard
+against resolving a certifi bundle that still trusts a compromised root.
+
+Background: in October 2026 the private keys of eight eMudhra intermediate CAs
+chaining to "emSign ECC Root CA - G3" were found to be trivially recoverable
+(Mozilla Bugzilla 2083449). certifi removed that root in 2026.10.18 and
+restored the unaffected emSign roots in 2026.10.19 (GHSA-6q48-6c7w-9gw2).
+"""
+
+import hashlib
+import os
+import re
+import ssl
+import sys
+from unittest.mock import patch, MagicMock
+
+import certifi
+import requests
+
+# Add the parent directory to the path so we can import from pystackql
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+
+from pystackql.utils import download
+
+# Minimum certifi release that distrusts the compromised root while keeping the
+# unaffected emSign roots. Must match the floor declared in pyproject.toml.
+MIN_CERTIFI_VERSION = (2026, 10, 19)
+
+# SHA-256 fingerprint of "emSign ECC Root CA - G3", the root that signed the
+# compromised eMudhra intermediates.
+DISTRUSTED_ROOT_SHA256 = (
+    "86a1ecba089c4a8d3bbe2734c612ba341d813e043cf9e8a862cd5c57a36bbe6b"
+)
+
+_PEM_BLOCK = re.compile(
+    r"-----BEGIN CERTIFICATE-----.*?-----END CERTIFICATE-----", re.S
+)
+
+
+def _bundle_fingerprints(path):
+    """Return the set of SHA-256 fingerprints (hex) of every cert in a PEM bundle."""
+    with open(path, "r", encoding="utf-8") as f:
+        data = f.read()
+    fingerprints = set()
+    for block in _PEM_BLOCK.findall(data):
+        der = ssl.PEM_cert_to_DER_cert(block)
+        fingerprints.add(hashlib.sha256(der).hexdigest())
+    return fingerprints
+
+
+class TestCertifiTrustStore:
+    """The resolved certifi bundle must not trust the compromised root."""
+
+    def test_certifi_meets_minimum_version(self):
+        """certifi must be at least the first release that distrusts the root
+        while retaining the unaffected emSign roots."""
+        installed = tuple(int(p) for p in certifi.__version__.split("."))
+        assert installed >= MIN_CERTIFI_VERSION, (
+            f"certifi {certifi.__version__} is older than "
+            f"{'.'.join(map(str, MIN_CERTIFI_VERSION))}; its CA bundle still "
+            "trusts emSign ECC Root CA - G3"
+        )
+
+    def test_bundle_is_non_empty_and_parseable(self):
+        """Sanity check so the fingerprint test cannot pass on an empty bundle."""
+        fingerprints = _bundle_fingerprints(certifi.where())
+        assert len(fingerprints) > 50
+
+    def test_bundle_excludes_compromised_emsign_root(self):
+        """emSign ECC Root CA - G3 must be absent from the bundle, checked by
+        certificate fingerprint rather than by the human-readable label."""
+        fingerprints = _bundle_fingerprints(certifi.where())
+        assert DISTRUSTED_ROOT_SHA256 not in fingerprints, (
+            "certifi bundle still contains emSign ECC Root CA - G3 "
+            f"({certifi.where()})"
+        )
+
+
+class TestRequestsUsesCertifi:
+    """The HTTPS client used for downloads must validate against certifi."""
+
+    def test_requests_default_ca_bundle_is_certifi(self):
+        """requests must resolve its default CA bundle from certifi, so the
+        certifi floor is what governs the download's trust store."""
+        assert os.path.realpath(requests.certs.where()) == \
+            os.path.realpath(certifi.where())
+
+    def test_download_file_does_not_disable_verification(self, tmp_path):
+        """download_file must never opt out of certificate verification."""
+        fake_response = MagicMock()
+        fake_response.headers = {'content-length': '4'}
+        fake_response.iter_content.return_value = [b'data']
+        fake_response.raise_for_status.return_value = None
+
+        dest = os.path.join(str(tmp_path), 'out.bin')
+        with patch('pystackql.utils.download.requests.get',
+                   return_value=fake_response) as mock_get:
+            download.download_file(
+                'https://releases.stackql.io/stackql/latest/x.zip',
+                dest, showprogress=False)
+
+        assert mock_get.called
+        assert mock_get.call_args.kwargs.get('verify', True) is not False